1. Field of the Invention
The present invention relates generally to orthopedic devices, and more particularly to an orthotic support for assisting in the stabilization and proper healing of ulcerative or pre-ulcerative conditions, plantar fasciitis or other conditions of the foot, especially for diabetic patients.
2. Background of the Invention
The present invention relates to orthotic or orthopedic devices that are used to immobilize, support and brace the foot and ankle. The sole or plantar surface of the foot is often subject to conditions or injuries, such as stone bruises, heel spurs, soft tissue injuries or injuries of the muscles, ligaments, bones or joints. Foot problems of this kind are often painful and exacerbated by the patient's need to walk during the healing process. The degree of immobilization and protection required varies with the severity and difficulty of the condition. Relief may sometimes be obtained by use of a molded inner sole or orthotic pieces in a regular shoe to add stiffness or alter the pressure distribution on the foot. Another option is custom made shoes which, although expensive, may provide relief for minor conditions. These may be augmented with the use of ankle braces or crutches but provide little relief for more serious conditions.
Diabetics are subject to especially severe and difficult foot problems. As the condition of diabetes gets worse, these patients begin to develop a problem called neuropathy, or polyneuropathy where they lose the sense of feeling in the plantar surface or bottom of the foot which may extend from the toes up the foot to the heel and eventually up to the lower leg or higher. Because there is no feeling, these patients are subject to severe pressure induced ulcerations that can be caused by high peak pressures or by hard foreign particles that may get in their shoe and which they do not realize are present. This often results in ulceration of delicate skin, which in diabetic patients is often very difficult to heal. Sometimes the festering ulcerations become infected, contain scar tissue and may result in secondary problems up to and including amputation. There were an estimated 54,000 amputations of this kind done in the United States in 1998. There are an estimated 23 million diabetics in the United States alone.
Prior art solutions have attempted to solve the problem by attempting to control the pressure on the bottom or sole of the foot. For example, a company called Royce Medical Company has modified their ordinary leg walker by replacing the normal Poron™ inner sole with about a ⅜ inch thick cross linked polyethylene foam inner sole material known as “plastazote” where the upper surface is cut into small hexagon shapes of roughly ⅜ inch across. One or more of the hexagonal areas directly under the ulceration or pressure site can be removed to create a reduction in pressure at the ulcer site itself. This can sometimes cause a distended wound because the exudate coming out of the ulcerated area causes a distention of the ulcer site which eventually granulates in to form scar tissue that has to be shaved off to avoid high pressure in that area when the foot is placed in a normal shoe. Removal of support under part of the sole of the foot tends to increase pressure loading of remaining portions of the foot which are supported. It also may cause increased pressure in the ring surrounding the cut away portion, which may restrict blood flow to the wound. Royce Medical Company is the owner of U.S. Pat. No. 5,464,385 entitled “Walker with Open Heel”.
Another example of the prior art approach is the walker produced by a company called Aircast, known as the Aircast Diabetic Walker™. To the ordinary walker they install a layer of about ½ inch to ⅝ inch thick cross-linked polyethylene foam referred to in the industry as “plastazote” foam in the bottom of the walker. It is a flat material which takes a compression set. While this does tend to distribute pressure over more of the foot to some extent, the support is still provided mainly by the boney prominences of the foot where the heel and ball of the foot fully compress the foam material. High unit pressure is found in those areas. We describe this result as producing a parabolic pressure distribution curve with a very high peak right under the boney areas.
Heretofore, the best available orthotic is a molded orthotic device which has been developed in the last several years using a technique called Total Contact Casting. Typically, a dressing is applied over the wound and then a piece of cotton or wool felt that will absorb exuding fluid is placed around the foot and held in place by a circularly knitted tubular material which is called a stockinet. Then, in one preferred method, a material called “conform”™ foam or “tempur”™ foam is used next. Approximately a ½ inch layer of this is placed under the arch and folded over the front of the toe down to the sides and pinched in on the sides creating somewhat of a cocoon below the ankle bones from the bottom of the foot up and over the forefoot. Over the top of this is wrapped some padding material for the cast which is either a cotton or polyester wool as is used for any other type of cast. Then a first layer of plaster or synthetic material is placed over the foot to form the cast and a wooden board is placed under the foot. Another layer of plaster or synthetic casting is plastered over the whole thing thus creating a “cocoon” for the foot. The “conform”™ foam or “tempur”™ foam has an open granular structure which compresses easily and rebounds extremely slowly. It will not sustain the body's weight without going to essentially zero thickness. We believe the Total Contact Cast nevertheless still produces a parabolic pressure distribution curve under the boney portions of the foot. Unfortunately, the total contact cast is heavy and not well designed for walking. The user has to pick the whole foot up and lay it down again, and it can only be used for about a week before it has to be removed and the foot cleaned and a new cast applied. The weight and bulkiness of the total contact cast create additional problems for diabetic patients. Patients can't remain immobilized to keep their weight off the cast. It is necessary for them to do some walking. Walking is beneficial because it actually stimulates the healing process. As a result, diabetics will start developing problems in other areas of their body because they are sensitive to pressure. Their tissues will break down at about half of what a young athlete can take without damage. The use of crutches can cause additional ulcers under the arms or on the hands.
Modern medical theories suggest that there may be some maximum threshold unit pressure if healing is to occur. If higher pressures are produced in “hot” spots, healing may take an extended time or be difficult to obtain at all. It appears that what might be called the time-pressure integral may also play an important role. The time-pressure integral relates to the cumulative effect of activity by the patient which produces pressures under all of the foot over a given time period.
Current theories suggest that ulcers will form in diabetic patients when peak unit pressure reaches 50 newtons per square centimeter (n/cm2). For comparison, simply walking in ordinary shoes that have a contoured inner sole matching the shape of the foot can generate unit pressures around 50-60 n/cm2. Running or suddenly changing direction will result in even higher unit pressures. Even diabetic shoes that contain a custom inner sole that is formed to match the patient's feet exactly are likely to generate unit pressures of 40-50 n/cm2, which can still allow ulcers to form.
In additional to being significantly more susceptible to ulceration, a diabetic patient will also generally take a significantly longer period for such ulceration to heal. It is not uncommon for it to take 10-12 weeks for an ulcer on the foot of a diabetic patient to heal when using Total Contact Casting. In comparison, such an ulcer would likely heal in less than seven days in a healthy individual. While maintaining unit pressures below 50 n/cm2 can minimize the formation of new ulcerations on the diabetic patient's foot, much lower unit pressures are necessary in order for the ulcer to heal properly and in a reasonable amount of time. Even below 50 n/cm2 sufficient damage is still being done to a diabetic individual's skin to delay or even completely prevent the ulcer from completely healing.
The requirements for shoe insoles are not well geared toward producing an insole that significantly minimizes the maximum and average unit pressure applied to the bottom of the foot. The purpose of a shoe insole is to provide the necessary support for the various flexion positions of the foot. Forces in the foot change dramatically during the various phases of a person's gait. For example, at heel strike an entire individual's weight is being applied at the heel of the foot. At this stage the purpose of the inner sole is to cup the heel. At mid-stance, the individual's weight is spread out more evenly across the foot and the inner sole must provide adequate support to the arch of the foot. During toe-off, the individual's weight is concentrated at the balls of the feet and the insole must be able to flex and stabilize the foot. The necessary type of support that must be provided by the inner sole of a shoe especially during heel strike and toe off is the lateral support of the foot to prevent it from over rotating.
A shoe insole must also be able to withstand the large forces that are applied to portions of the inner sole at various phases of a person's gait without breaking down or becoming permanently compressed. An inner sole of a shoe accommodates the relatively large forces that are applied to the heel and the ball of the foot during certain phases of the gait by increasing the amount cushioning at those locations. This does attempt to minimize to some extent the magnitude of the peak forces that are applied to the foot, but does nothing to spread out the force over the entire surface of the foot. As a result, inner soles of shoes result in a significant parabolic force distribution curve, where peak pressures are significantly higher under the bony portions of the foot, even those that are contoured and that have upper layers designed to cushion the foot.
In order to achieve these purposes, the inner soles of shoes use relatively hard and dense materials to provide sufficient support over time, even for the relatively “soft” upper layers that are designed to cushion the foot. If the inner sole were made of a material that is too soft, the inner sole would flatten over a relatively short period of time due to the large peak pressures that occur at various portions of the gait cycle and would quickly lose the ability to provide any support or cushioning.
In addition to the increased likelihood of ulceration, a certain percentage of diabetic patients will also develop what is referred to as charcot condition. This is a hyper-circulation condition where the bones become very fragile. The bones go through a cycle of fracturing and healing that results in the loss of neural control and ultimately the bone degrades and crumbles. In the foot, the balls and heal of the foot degrade such that the fascia over the mid-sole will stick out below the heal and ball, sometimes referred to as rockerbottom charcot. Also, the cycling can cause calcification on the bone. This can result in a growth on the bony protrusion on the inside of the foot by the arch, giving the side of the foot somewhat of a “V” shape. Special consideration must be taken into account when designing a walking boot for diabetics that have charcot condition, such that the inner sole accommodates the differing contours of the foot and does not result in the creation of point pressures. This is generally accomplished by cutting away some of the foam insole in order to accommodate the deformity in the foot.
It would be desirable to have a walking boot which can be used over an extended period of time and which improves upon the attributes of the total contact cast by reducing the peak plantar pressure operating on the injured foot while walking in the walker. We have demonstrated such an improvement with a new approach that utilizes the arch and side areas of the periphery of the foot to support part of the load on the foot and reduce the maximum peak pressure under the sole of the foot.